This study aimed to evaluate the effect of radial artery cannulation on hand perfusion in patients with normal modified Allen's test undergoing cardiac surgeries using cardiopulmonary bypass (CPB).Prospective follow-up study.Single institution, Assiut University Cardiothoracic Hospital.Forty-nine patients who underwent cardiac surgeries using cardiopulmonary bypass were enrolled.Cannulation of radial artery in the dominant hand using a 20-gauge catheter.The primary outcomes were the mean peripheral perfusion index (PPI)60 seconds (mean PPIIn adult patients undergoing cardiac surgeries using CPB, even with normal modified Allen's test, radial artery cannulation may affect the perfusion of the dominant hand, especially at low arterial blood pressure or low core body temperature. Since the PPI is one of the noninvasive methods used for intraoperative assessment of the peripheral perfusion, the authors recommend the use of the noncannulated hand for this purpose to not misguide this assessment.